1. Field of the Invention
The present invention relates generally to a fuel injector for an internal combustion engine and more particularly to a sensor which is disposed in the fuel injector for sensing the lift timing of the valve element thereof and outputting a signal indicating the injection timing.
2. Description of the Prior Art
In a known arrangement, a pressure sensitive piezoelectric element has been placed within the fuel injector in a manner to be subject to compression upon an opening movement of the needle valve or the like controlling the injection orifice of the injector nozzle, and thus functions as a lift or timing sensor. This piezoelectric element has been provided with a pair of lead lines which serve to establish an operative connection between the piezoelectric element and a control circuit utilized for varying the injection timing.
However, this arrangement suffers from the drawback that the provision of the lead lines complicates the construction of the arrangement to the point where it is difficult to apply force evenly over the surfaces of the element, which leads to cracking of same and the subsequent infiltration of fuel (e.g. diesel oil) into the regions where the lead wires are connected to the piezoelectric element. Further, breakage of one or both of the relatively fine lead wires as a result of injector and engine vibration is apt to occur, which renders the sensor inoperative and creates a situation where the output of the piezoelectric element is apt to short circuit and flow to the needle valve of the injector, break the fuel film between the valve and the associated portion of the injector valve (viz., the valve seat) and induce highly undesirable electrolytic corrosion of one or both of the needle valve and the valve seat.
Moreover, the complex construction involving the lead wires increases the time and trouble that must be taken during assembly and/or repair of the injectors, inducing unwanted increases in both production and maintenance costs.